The proper segregation of genetic information at cell division is essential for viability of the newly formed cells and in multicellular organisms for viability of the organisms. In eukaryotes, the segregation of gentic information during cell division is mediated by the mitotic spindle, a transient and dynamic supramolecular structure. Improper function of the spindle during mitosis can result in aneuploidy and cell death. Failure of proper spindle function in the related process of meiosis results in the human disorder of Down's syndrome. A thorough understanding of mitosis requires a complete knowledge of the molecular participants of this process. It is with this in mind that we propose to study the bimD gene of Aspergillus nidulans. The bimD gene was identified as a temperature sensitive mutation leading to a block in mitosis (bim). The block in mitosis caused by the bimD5 mutation results in a spindle lacking kinetochore microtubules. We will clone the bimD gene by complementation of its recessive temperature sensitive phenotype and isolate cDNA to determine its sequence. We will identify the protein and its cellular location by obtaining polyclonal antisera to fusion proteins made in E. coli with the cDNA. We will isolate and characterize extragenic suppressor mutations to the bimD5 mutation to identify other genes that interact with bimD. A full characterization of bimD will extend our knowledge of kinetochore and kinetochore microtubule functions in mitosis.